The present invention relates to the removal of sulfur dioxide and sulfur trioxide from flue gases, particularly from flue gases emitted from furnaces for the manufacture of glass. In the current regulatory environment, a significant portion of the cost of doing business in many industries is that incurred in complying with the environmental regulations of the jurisdiction in which the industry is operating. In some industries, notably the utility industry, this requirement is a major irritant and may have an effect on profitability, but it is not likely to affect the very survival of a company in the industry. The increased costs are, at least to some extent, passed along to the consumer. There are other industries, however, that do not enjoy this assurance of profitability, and competition from companies in less strict jurisdictions may well force a company in the stricter jurisdiction to go out of business for no other reason than that it has a greater cost of complying with environmental regulations. For example, if a glass company in one jurisdiction is required to use fuel with a lower sulfur content than that which glass companies in adjacent jurisdictions are permitted to use, the difference in fuel costs may well be the deciding factor in the company's survivability. Accordingly, it would be desirable for a glass company in a relatively strict jurisdiction to be able to demonstrate that it is using a process that produces sulfur emissions with a less expensive high-sulfur fuel that are as low as emissions ordinarily encountered with a more expensive lower-sulfur fuel.
A process for achieving this result was proposed in Hirota, U.S. Pat. No. 3,944,650. In Hirota, the flue gases are passed through a waste heat boiler and then through a spray tower having two levels of spray and a glass-fiber demister for wet scrubbing the flue gases. The spray used in the spray tower is an aqueous solution of sodium hydroxide, sodium carbonate, or sodium sulfite, which reacts with the oxides of sulfur in the flue gases to produce sodium sulfate, sodium sulfite, or sodium bisulfite. The solutions are continuously recycled but are periodically removed from the cycle for a rather elaborate course of treating to convert the aqueous sodium sulfite to the solid sodium sulfate used in glass manufacture. It is necessary in the Hirota process that the flue gases be kept saturated, which results in the necessity of using the demister. At the outlet of the desulfurization process, it is also necessary in the Hirota method to reheat the clean wet flue gases in order to provide enough buoyancy for the gases to rise from the stack rather than settle quickly to the ground.
Whatever the operational results in the Hirota method may be, it is apparent that the capital requirements are not inconsiderable. Accordingly, it would appear that the financial advantage gained by using higher-sulfur fuel is somewhat compromised by the capital and operating expenses involved in using the method. It is apparent, therefore, that a method is needed for lowering the sulfur oxide content of glass-furnace flue gases that does not require a large capital investment.